ox: Ignore statistics cookies with stat:nil

* lisp/ox.el (org-export--prune-tree): Fix bug preventing pruning within
  secondary strings.

* testing/lisp/test-ox.el (test-org-export/handle-options): Update test.

Reported-by: Thomas S. Dye <tsd@tsdye.com>
<http://permalink.gmane.org/gmane.emacs.orgmode/100999>

lisp/ox.el

@@ -2631,13 +2631,12 @@ from tree."
 		      ;; If headline is archived but tree below has to
 		      ;; be skipped, remove contents.
 		      (org-element-set-contents data)
-		    ;; Move into secondary string, if any.
-		    (let ((sec-prop
-			   (cdr (assq type org-element-secondary-value-alist))))
-		      (when sec-prop
-			(mapc walk-data (org-element-property sec-prop data))))
 		    ;; Move into recursive objects/elements.
-		    (mapc walk-data (org-element-contents data)))))))))
+		    (mapc walk-data (org-element-contents data)))
+		  ;; Move into secondary string, if any.
+		  (dolist (p (cdr (assq type
+					org-element-secondary-value-alist)))
+		    (mapc walk-data (org-element-property p data)))))))))
     ;; If a select tag is active, also ignore the section before the
     ;; first headline, if any.
     (when selected

testing/lisp/test-ox.el

@@ -595,11 +595,11 @@ Paragraph"
 			   nil nil nil '(:with-properties ("B"))))))
   ;; Statistics cookies.
   (should
-   (equal ""
+   (equal "* Stats"
 	  (let (org-export-filter-body-functions
 		org-export-filter-final-output-functions)
 	    (org-trim
-	     (org-test-with-temp-text "[0/0]"
+	     (org-test-with-temp-text "* Stats [0/0]"
 	       (org-export-as (org-test-default-backend)
 			      nil nil nil '(:with-statistics-cookies nil)))))))
   ;; Tables.